Method of strenghtening a felt web



United States Patent 11 Claims. cl. 156-209) ABSTRACT OF THE DISCLOSURE A felt-like web including polyamide fibers cross-secting and contacting each other is strengthened by wetting the web with a liquid containing at least one of p-hydroxybenzoic acid octyl ester and benzenesulfonic acid butylamide as a softener for the polyamide fibers, the liquid and the softener being volatilizable at an elevated temperature sufficiently low so as to have no adverse effect on the polyamide fibers. The wetted web is then heated at such relatively low volatilization temperature so that the polyamide fibers will be softened and cross-secting, contacting portions thereof will be adhered to each othre, while simultaneously the liquid and softener will be volatilized and thus removed from the web.

The present invention relates to a process for making fleece materials or needle felts which consist totally or at least partly of polyamide fibers and, more particularly, the present invention is concerned with a method of producing such fleece or felt wherein the individual polyamide fibers at their cross-secting or contacting points are adhered to each other without incorporation of an ex traneous binding agent into the felt or fleece.

It has been proposed to dissolve surface portions of polyamide fibers with phenol and to adhere contacting slightly dissolved surface portions to each other. However, special precautions have to be taken in carrying out this process and consequently the same is rather costly.

It has also been proposed to wet polyamide fibers with a zinc chloride solution and thereafter to heat the wetted web to an elevated temperature at which hydrochloric acid will be formed. The hydrochloric acid has a dissolving effect on the polyamide fibers and this again will lead to adhesive adherence of contacting polyamide fibers. After a subsequent drying process, the fibers are thus adhered to each other. Here again, special precautions must be taken in view of the formation of hydrochloric acid and, furthermore, the fleece or felt material must then be freed of residual acid.

It is therefore an object of the present invention to overcome the above-discussed disadvantages and difficulties in strengthening felt-like bodies or webs which consist at least partly of polyamide fibers.

It is a further object of the present invention to adhere to each other contacting portions of cross-secting polyamide fibers of a felt or fleece consisting at least partly of polyamide fibers, in a manner which is simple, effective and relatively inexpensive.

Other objects and advantages of the present invention will become apparent from a further reading of the description and of the appended claims.

With the above and other objects in view, the present invention contemplates a method of strengthening a feltlike web consisting at least partially of polyamide fibers cross-secting and thus contacting each other, comprising the steps of wetting the felt-like web with a liquid containing a softener for the polyamide fibers, the liquid and the softener being adapted to be volatilized at an elevated temperature sufficiently low so as to have no adverse effect on the polyamide fibers, and heating the thus wetted web at the elevated temperature so as to soften the poly amide fibers thereby adhering cross-secting portions of the polyamide fibers to each other at their points of contact, and also volatilizing the liquid and the softener, whereby the polyamide fibers are adhered to each other and the felt-like web is strengthened thereby without incorporating a binding agent in the web.

It was thus found that the difiiculties of the prior art could be avoided according to the present invention by wetting the polyamide fibers of the felt-like structure with emulsions or solutions of certain aromatic esters which act as softeners for polyamide fibers, so that the thus wetted polyamide fibers will be adhesively adhered to each other at their contact points upon being subjected to an elevated temperature of preferably between and C. Very fine, in fact, nearly microscopic points of adhesion are formed in this manner between contacting portions of cross-secting polyamide fibers. A highly unexpected increase in the strength of the felt-like structure without impairment of the textile characteristics of the fibers, is achieved.

It is thus possible to produce in a continuous manner for instance fleece materials and needle felts with a weight of between 50 and 1500 grams per square meter. The thus produced non-woven materials possess very marked textile, fabric-like properties. They have a high degree of tear resistance and abrasion resistance, and are of low specific weight, high air permeability, crease resistant and highly resilient.

Of the aromatic esters which act as softeners for polyamide fibers, particularly the ester formed of p-oxybenzoic acid and of 2-ethylhexanol has been found to be highly suitable. The esterification product of these two reactants is the p-hydroxybenzoic acid octyl ester of the formula HOC H -COOC H Another suitable softener which, however, has to be applied in a higher concentration is the benzenesulfonic acid butylamide of thfi formula C6H5SO2NHCH2CH2CH2CH3.

It is a further advantage of the method of the present invention that it is possible, in a continuous manner, during the adhesive adhering of the polyamide fibers of the fleece or needle felt, to permanently deform the same.

When it is desired to otbain a material of high flexi bility, then, the felt or fleece should not consist exclusively of polyamide fibers, but rather of a mixture of polyamide fibers and other synthetic fibers, for instance up to 40% polyester or polyacrylonitrile fibers. These other fibers will not be softened by the emulsion or solution of esters such as the two esters mentioned above, and thus the proportion of points of adhesion within the fleece or felt will be reduced without substantial effect on the tear and abrasion resistance of the treated non-woven web or fabric.

The following examples are given as illustrative only, without limiting the invention to the specific details of the examples.

Example 1 50% polyamide fibers of 3 denier and a staple length of 60 mm. are mixed with 50% polyamide fibers of 5 denier and a staple length of 40 mm., and of this mixture a cross-layer fleece or a fleece with a random distribution of the individual fibers is produced. The thus formed fleece is then needled so as to preliminarily strengthen the web to the extent required for subjecting the same to wetting in a padding machine or padder with a softener emulsion.

The softener emulsion consists of 10 parts by weight p-oxybenzoic acid octyl ester, 5 parts by weight con- 3 centrated aqueous ammonia and 150 parts by weight water.

The needled and wetted fleece is squeezed so as to reduce the liquid content thereof to between 100 and 200% of the weight of the dry fleece, and is then dried at between 100 and 160 C. in a suction drum drier. Thereby, adhesive adherence of contacting points of the cross-secting polyamide fibers will be achieved while the softener will be quantitatively volatilized. The softener vapors are then cooled and condensed in an air outlet conduit and can be recovered with a yield of up to about 90%.

Example 2 The process of Example 1 is carried out. However, the softener emulsion is replaced by a softener solution consisting of parts by weight p-oxybenzoic acid octyl ester, 70 parts by weight methanol and 30 parts water.

Example 3 The process of Example 1 is carried out. However, a perforated member having an outer surface corresponding to the desired final shape of the felt or fleece is fixed to the surface of the suction drum so that the loose, wetted and needled fleece will adhere by suction to the outer surface of this perforated member without forming any folds. Again, the contacting points of the polyamide fibers are adhered to each other by heating to between 100 and 160 C., and in this simple manner which also lends itself to continuous operation shaped high strength felt-like materials and fleece bodies of different curvatures can be produced. The thus obtained deformation of the fleece or felt is irreversible.

Examples 4-6 The processes described in Examples 1-3 are repeated, however, the 10 parts by weight of p-oxybenzoic acid octyl ester are replaced by 20 parts by weight of benzenesulfonic acid butylamide.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features, that from the standpoint of prior art, fairly constitute essential char-- acteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A method of strengthening a felt-like web consisting at least partially of polyamide fibers cross-secting and thus contacting each other, comprising the steps of wetting said felt-like Web with a liquid containing a softener for said polyamide fibers, said softener being selected from the group consisting of p-hydroxybenzoic acid octyl ester and benzenesulfonic acid butylamide, said liquid and said softener being adapted to be volatilized at an elevated temperature sufficiently low so as to have no adverse effect on said polyamide fibers; and heating the thus wetted web at said elevated temperature so as to soften said polyamide fibers thereby adhering cross-secting portions of said polyamide fibers to each other at their points of contact, and also volatilizing said liquid and said softener, whereby said polyamide fibers are adhered to each other and said felt-like web is strengthened thereby without incorporating a binding agent in said web.

2. A method as defined in claim 1, wherein said liquid containing said softener is an emulsion.

3. A method as defined in claim 1, wherein said liquid containing said softener is a solution.

4. A method as defined in claim 1, wherein said elevated temperature is between about and C.

5. A method as defined in claim 1, wherein said softener is p-hydroxybenzoic acid octyl ester.

6. A method as defined in claim 1, wherein said softener is p-hydroxybenzoic acid octyl ester and is present in an amount equal to about 10% of the weight of said liquid.

7. A method as defined in claim 1, wherein said softener is benzenesulfonic acid butylamide.

8. A method as defined in claim 1, wherein said softener is benzenesulfonic acid butylamide and is present in an amount equal to about 20% of the weight of said liquid.

9. A method as defined in claim 1, wherein simultaneously with said heating of said wetted web the latter is subjected to mechanical deformation so that said web is strengthened in the thus-deformed state.

10. A method as defined in claim 1, wherein continuously successive portions of said felt-like web are wetted with said softener-containing liquid.

11. A method of strengthening a felt-like web consisting at least partially of polyamide fibers cross-secting and thus contacting each other, comprising the steps of wetting said felt-like web with a liquid containing a softener for said polyamide fibers adapted to soften and to make the same actively adhesive at an elevated temperature of between 100 and 160 C.; said softener being selected from the group consisting of p-hydroxybenzoic acid octyl ester and benzenesulfonic acid butylamide; and heating the thus wetted web at said elevated temperature so as to soften said polyamide fibers and to adhere cross-secting portions thereof to each other thereby strengthening said felt-like web.

References Cited UNITED STATES PATENTS 2,365,931 12/1944 Benger 8-136 2,380,003 7/1945 Whitehead 156-307 X 3,053,609 9/ 1962 Miller 156-307 X 3,117,362 1/1964 Breen 161-227 X 3,309,254 3/1967 Rowe 156-240 HAROLD .ANSHER, Primary Examiner. 

